
One of our bitches (who of the two sisters we kept from that litter, I'd have expected to be the one to have good sized litters!) produced two in her first, male and female, and a singleton (bitch - how often are singleton puppies male!!) in her second and last litter. We sold both the two from her first litter having run on the bitch but by that time her sister had produced her litter which was 'better' and I had to watch numbers. The singleton puppy we kept. Because I felt so sorry for her sitting alone in her ex-pen after mum had decided to have nothing more to do with her (she was fully weaned by then), I tended to carry her around with me, for as long as her size would allow. As a result, she was spoilt rotten, and as she grew up, she became very much the matriach of my small pack - even her mum deferred to her. She wasn't 'nasty' but it was clear her early status, with me, stuck. Nobody messed with her to the day we had to say goodbye. In reality, she wasn't really good enough to show or breed from and as she started having seasons at 5 monthly intervals (no way!) I had her spayed. So she was very much a passenger, but much loved despite that.
Our first litter was a singleton, male, but there were 2 - we lost the other one due to my inexperience. He went to a pet home and eventually as they moved up there, spent most of his days up in Moose Factory (North Canada).
If you know your bitch only has one puppy, be aware - small 'litters' often sit beyond the normal pregnancy time and she may need help to get things started. Also watch her 'milk bar'. With just one puppy to provide for, she could become engorged (I made sure I rotated my singleton puppies so the teats were drained regularly) - mastitis risk. Also you won't need to be feeding her anything like as much as she'd need with a full-sized litter. I was in panic when with my first litter, my bitch virtually stopped eating, drinking yes, but she wasn't really interested in much food. Nature knew she only had the one (or two originally) puppy to provide for so I need not have worried. And the vet was involved in the one I managed to lose, so I knew she was empty.
Good luck because having just the one will mean, maybe, more work than having a normal litter, in some ways.
ps Good point about heating...... not having mum or siblings to snuggle up to (when mum needs out) means you must have external heating so the whelping box is kept at around 80F or higher. Newborn puppies can't regulate their own heat/temperature.